sync_cor.c

来自「TI的DSP C55X的应用程序」· C语言 代码 · 共 308 行 · 第 1/2 页

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/* External Data */

/* Code */

int sync_corr( int *I_SRC, int *Q_SRC, int *filt )
{
    int     i, j, sync_point,index, corr_mag, max, I_temp, Q_temp;
    int     *sync_ptr, *rc_data, sync_i, sync_q, rc_i, rc_q;        
    long    I_ltemp, Q_ltemp;    

/**************************************/
/* Filter just enough data to span    */
/* correlation window                 */
/*                                    */
/* Store resultant 76 I,Q pairs       */
/* into temp_rc[] storage.            */
/**************************************/

    rc_data = temp_rc;  /* Set pointer to temporary storage for filter output */
    
    I_SRC += 8;         /* Intentional offset to start 2 symbols */
    Q_SRC += 8;         /* to left of expected sync point.       */
    
    for (i = 0 ; i < 76 ; i++)
    {
        I_ltemp = _lsmpy((*(I_SRC++)), (*filt) );
        Q_ltemp = _lsmpy((*(Q_SRC++)), (*filt++) );
        for (j = 47 ; j > 0 ; j--)
        {
            /* I_temp += (*(I_SRC++)) * (*filt); */
            /* Q_temp += (*(Q_SRC++)) * ((*filt++)); */; 
            I_ltemp = _smac(I_ltemp, (*(I_SRC++)), (*filt) );
            Q_ltemp = _smac(Q_ltemp, (*(Q_SRC++)), (*filt++) );
        } 
        
        filt  -= 48;    /* Set Filter pointer back to start */
        
        I_SRC -= 47;    /* Start 1 sample over next time */
        Q_SRC -= 47;
        
        *(rc_data++) = (I_ltemp>>18);   /* Store Filter Output I term in Q13 format */
        *(rc_data++) = (Q_ltemp>>18);   /* Store Filter Output Q term in Q13 format */
    }

/****************************************/
/* Correlate with Sync Word for Slot #0 */  
/* Keep track of correlation peak.      */
/****************************************/

    max = 0;                    /* Correlation Magnetude Maximum */
    
    sync_point = 0;             /* Index into data to sync point */
     
    rc_data = temp_rc;          /* Set pointer to beginning of filtered data */
    
    for (i = 0 ; i < 16 ; i++)
    {  
      /* Zero resultant correlation vector components */
        I_ltemp = 0;
        Q_ltemp = 0;                              
        
      /* Point to M.E.P. buffer for slot #0 Sync word */    
        sync_ptr = cor_sync;    
     
      /* Perform Correlation at offset 'i' into data */
        for (j = 15 ; j > 0 ; j--)  
        {
            sync_i = *(sync_ptr++);
            sync_q = *(sync_ptr++);
            rc_i   = *(rc_data++);
            rc_q   = *(rc_data++); 
            rc_data += 6;
            I_ltemp = _smac(I_ltemp, sync_i, rc_i);
            I_ltemp = _smac(I_ltemp, sync_q, rc_q); 
            Q_ltemp = _smac(Q_ltemp, sync_i, rc_q);
            Q_ltemp = _smas(Q_ltemp, sync_q, rc_i); 
        }
        rc_data -= 118;  /* 120 would set pointer back to start              */
                         /* we will start 1 sample (I,Q pair) over next time */

      /* Compute Correlation Magnetude & Maximize */
        /* corr_mag = (float)sqrt(I_temp*I_temp + Q_temp*Q_temp); */
		I_temp = (I_ltemp>>16);
		Q_temp = (Q_ltemp>>16);
		
		I_ltemp = _lsmpy(I_temp, I_temp);
		I_ltemp = _smac(I_ltemp, Q_temp, Q_temp); 
		index = (I_ltemp>>16);
 		corr_mag = sqrt_tab[index>>5];

        if( corr_mag > max )
        {
            sync_point = i;
            max = corr_mag;
        }
    }
    
    return( sync_point + 8 );   /* Note that we started at offset = 8 */
}